Enabling bare die liquid cooling for the bare die and hot spots

ABSTRACT

A liquid cooling device for a die including a support block supporting a plurality of substantially vertical channels transporting fluid to and from a bare die surface for heat removal. The device is mounted on top of a bare die using a frame or spring. In another embodiment, the device allows thermoelectric cooling of a dedicated fluid line.

BACKGROUND

As processing power continually increases with advances inmicroprocessor technology, the heat that is produced increases. Manysolutions seek to improve cooling of the die. Current micro-channeltechnology uses a thermal interface material (for example, TIM1) whichis a major contributor to thermal resistance. Also the currentmicro-channel flow length and the heat capacity of the coolant (massflow×specific heat) have the most significant impacts to thermalresistance. Often, the fluid boundary length is long. Another solutionproposes to spray liquid over the die. However there are drawbacks tothat implementation as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The claimed subject matter will be understood more fully from thedetailed description given below and from the accompanying drawings ofthe disclosed embodiments which, however, should not be taken to limitthe claimed subject matter to the specific embodiment(s) described, butare for explanation and understanding only.

FIG. 1 is a cross-sectional schematic diagram showing one embodiment.

FIG. 2 is an enlarged view showing fluid flow according to oneembodiment, taken from View B of FIG. 1.

FIG. 3 is a top view of one embodiment.

FIG. 4 is a cross-sectional view of one embodiment, taken from line A-Aof FIG. 1.

FIG. 5 is a cross-sectional schematic diagram showing one embodiment,including a dedicated fluid line.

FIG. 6 is a top view schematic diagram showing one embodiment, includinga dedicated fluid line.

FIG. 7 is a cross-sectional schematic diagram showing one embodiment.

DETAILED DESCRIPTION

According to one embodiment, FIG. 1 shows a schematic of a liquidcooling device 10 including a support block 12 supporting cooling lines14 in thermal communication with a bare die 16. The cooling lines 14 areconfigured to remove heat directly from the bare die 16 by transportingfluid to and from the surface of the bare die. By allowing directcontact between the fluid and the die, a cold plate is not required.

The liquid cooling device 10 may include a frame 18 coupling the supportblock 12 to a substrate 20 (for example, a semiconductor). The bare dieis also coupled to the substrate 20 via solder balls and underfillmaterial 22, attached to the bottom surface of the die. The bare die mayalso be coupled to the substrate using electrical connections, includingsoldered or conductive adhesive connections, or using other surfacemount packaging technologies for integrated circuits.

The cooling lines 14 may be a singular, long, continuous line containingand circulating fluid in device 10. In one embodiment, the cooling linesinclude various segments of circulating fluid. These segments are brokendown and named in this specification as an aid in describing thestructure of one or more embodiments, and are not intended to belimiting. Further, the segments may be referred to in the singular orplural and are also not meant to be limited to that which is shown ordescribed.

In one embodiment, the cooling lines may be closed-loop as fluidrecycles in the device. In another embodiment, the cooling lines may beopen-loop. Additional components such as heat exchangers and pumps maybe coupled to the device and used to cool and circulate the fluid,respectively. Further, coolants with various heat capacities may be usedas fluid for circulation in the cooling lines.

As shown in FIG. 1, the row of circles labeled 24 are referred to as“inlet pipes”, and the lower row of circles labeled 26 are referred toas “outlet pipes”. Both inlet pipes 24 and outlet pipes 26 are segmentsof the cooling lines 14, and the flow of the fluid through these pipesis perpendicular to the plane of the figure, as will be furtherdescribed below. The inlet pipes may be positioned at a higher levelthan the fluid outlet pipes, such as shown in the figure. In oneembodiment, the inlet pipes and the outlet pipes are positioned at thesame height.

As the arrows indicate, fluid is transported downward from the inletpipes 24 to the bare die 16 through a segment 28 referred to as an“inlet portion”. The fluid traveling upward from the bare die 16 to theoutlet pipes 26 traverses a segment 30 referred to as an “outletportion”. These two segments of inlet portions and outlet portions arealso referred to as vertical channels.

It may be noted that in general, the flow of the fluid follows thedirection of the arrows as indicated. In some locations or situations,the fluid flow may be non-uniform and deviate from the general directionof flow.

FIG. 1 further shows an area 32 in which a sealant may be used to fillin between the support block 12, bare die 16 and substrate 20. Thesealant may include epoxy, neoprene, and other suitable materials tostop leaks, add structural support, and/or enable permanent attachment.

Referring to FIG. 2, an enlarged view showing fluid flow according toone embodiment, taker from View B of FIG. 1, is shown at 40. Referringin particular to vertical channel 42, the fluid travels downward throughthe inlet portion 28, contacts the bare die surface 44 to remove heat,and travels upward through the outlet portion 30, as described above.The vertical channel further includes a heat transfer region 46connecting the inlet portion 28 with the outlet portion 30 and routingthe fluid so that it transitions from a downward direction to an upwarddirection.

In describing one or more embodiments, there are references toorientation and direction. It should be understood that these referencesare used to aid in understanding the relationships between componentsand fluid flow, and are not meant to be limiting in any way. Forexample, vertical channels do not necessarily need to be orientedvertically, such as the case with a closed system where the flow will bepressurized.

The fluid traversing vertical channel 42 contacts an area 48 on thesurface of the bare die and removes heat from that area. Additionalvertical channels adjacent to vertical channel 42, such as 50 and 52,may each be in thermal contact with a respective surface area on thebare die. In one embodiment, the entire bare die surface may be coveredwith vertical channels for cooling of the entire die. Alternatively,only select regions are covered with vertical channels.

The vertical channels may include walls dividing the fluid flow toreduce the fluid boundary length. In one embodiment, a vertical channelshares a wall with an adjacent vertical channel. For example, verticalchannel 42 shares one wall 54 with vertical channel 50 and one wall 56with vertical channel 52. These common walls extend from the outlet pipeto the surface of the bare die.

Another type of wall is referred to as a separation wall which is in thevertical channel for separating the fluid traveling to the bare die fromthe fluid traveling away from the bare die. As shown, separation wall 58does not extend all the way down to the bare die, but instead leaves agap between the end of the separation wall and the bare die surface,thus allowing room for the fluid to flow from the inlet portion to theoutlet portion. As the fluid goes around the separation wall, from theinlet portion into the heat transfer region and up the outlet portionsuch as indicated by the arrows, the fluid removes heat from the baredie.

In this exemplary embodiment, the walls are less than 10 μm inthickness. The wall thickness may also be greater than 10 μm dependingon other device parameters. The walls may be pressed onto the diesurface. They may also be fastened using an adhesive or other method.Walls may be temporarily affixed on or permanently attached to the baredie surface.

The configuration described above brings about a short heat transferregion length and the flow over the bare die surface results in thinthermal and hydrodynamic boundary layers. This condition yields veryhigh local heat transfer coefficients, indicating that thermalcommunication between the bare die and the fluid is good, enablingefficient cooling.

A simulation was performed using a computational fluid dynamics softwareprogram called Icepak, made by ANSYS, Inc. of Canonsburg, Pa., todetermine the feasibility of obtaining high heat transfer coefficientsin a configuration similar to the one described above. For exemplarypurposes, the channel dimensions were set to 50 μm×50 m with aseparation plate 10 μm thick. The equivalent heat flux was 100 W/cm² andthe inlet velocity 1 m/s. The results showed a pressure drop ofapproximately 60 kPa, well within the capability of a gear pump (thusthe boundary conditions were realistic). The resulting heat transfercoefficient variation was on the average over 100,000 W/cm², which maybe equivalent or better than that of the current macro or microchannels.

Turning to FIG. 3, a top view of one embodiment is shown at 70. Inaccordance with the figure and similar to the embodiment of FIG. 1, thesupport block 12 holds segments of the cooling lines, specifically thevertical channels (not visible), which are capable of transporting fluidfrom the inlet pipes 24 down to the bare die and back up to exit at theoutlet pipes 26. In one embodiment, the cooling lines further include aninlet manifold 72 that delivers fluid to all of the inlet pipes 24 andan outlet manifold 74 that receives fluid from all of the outlet pipes26.

In this exemplary embodiment, the inlet pipes 24 and the outlet pipes 26alternate in a parallel configuration. As the flow of fluid in the inletpipes 24 heads toward the general direction of the outlet manifold 74,the inlet portions 28 of the vertical channels are fed, as will be moreapparent below. After entering the inlet portions, the flow traversesthe outlet portions of the vertical channels and feeds the outlet pipes,where the flow is toward the general direction of the outlet manifold.

Typically, the cooling lines on an inlet side (top) of the liquidcooling device will start off cool and after thermal communication withthe bare die surface, the cooling lines on an outlet side (bottom) ofthe device will be warmer. Fluid collecting in the outlet manifold isgenerally significantly warmer than the fluid entering the inletmanifold. Generally, in a closed system, fluid exiting the outletmanifold 74 may be routed to a heat exchanger or other heat removaldevice (not shown) before the fluid recycles and reenters the inletmanifold 72.

Referring to FIG. 4, a cross-sectional view of one embodiment taken fromline A-A of FIG. 1 is shown at 80. (It is noted that this embodimentslightly differs from that of FIG. 1.) Looking up toward the top fromthe cross-section, the frame 18 surrounds the support block 12 whichsupports a grid 82 of vertical channels. As described above and shown inthe figure, one or more vertical channels include an inlet portionrouting fluid to the die and an outlet portion routing fluid away aftercontacting the die. As depicted in FIG. 4, for example, as fluid iscirculating, the fluid flows through the inlet portion 28 (out of thepage) to the outlet portion 30 (into the page) at vertical channel 42.Adjacent to vertical channel 42 on the left side is vertical channel 50,and on the right side is vertical channel 52. As seen from FIGS. 1-4,fluid in vertical channels 50, 42, and 52 are delivered by differentinlet pipes and the fluid exit via different outlet pipes. In thecolumns (up and down, referenced to the page) of vertical channels,fluid is supplied by the same inlet pipes and is returned to the sameoutlet pipes, that is, each column of squares is tied to the same inletpipe or outlet pipe.

Referring back to FIG. 4, the squares cross-sections as indicated by thegrid 82 correspond to individualized bare die surface areas. Asmentioned above, the vertical channels separate flow to ensure smallboundary length for the fluid as it flows by the bare die surface areas.

Although the vertical channels are shown to have square cross-sections,the channels may be individual tubes and may have circular or othershaped cross-sections. The vertical channels may also be arranged in adifferent pattern and not necessarily in a grid configuration. Forexample, certain areas of the die may not need cooling, therefore wallsand vertical channels are not needed in those areas.

Referring to FIG. 5, one embodiment for a liquid cooling device 90provides a separate dedicated fluid line 92 for isolating a hot spot 94.Hot spots are known areas on the bare die in need of extra heatdissipation or higher rate of heat dissipation. It may be useful toidentify the hot spots and target them for more efficient cooling of thedie.

The liquid cooling device 90 may be similar in configuration to theembodiments shown in FIGS. 1-4. A support block 96 is configured tosupport a system of cooling lines 98 and may be mounted to a bare die100 and substrate 102 via a frame 104. The die and the substrate arecoupled by solder balls and underfill material 106. The support blockmay be attached to the substrate and leaks may be prevented byapplication of epoxy at 108. Cooling lines 98 include segments such asinlet pipes carrying fluid to inlet portions of vertical channels and toheat transfer regions where the fluid touches the surface of the baredie and removes heat. The cooling lines further include outlet portionsof vertical channels to remove the heated fluid and join with outletpipes that take the fluid away from the die.

Dedicated fluid line 92 is a fluid conduit separate from the coolinglines depicted in FIGS. 1-5. As seen from FIG. 5, this fluid line isdedicated to transporting fluid to and from the hot spot 94. Thededicated fluid line has a vertical channel through which fluid canreach the hot spot and remove heat. Dedicated fluid line 92 furtherincludes an inlet line 110 routing fluid to the vertical channel and anoutlet line 112 routing fluid away from the vertical channel.

At 120, FIG. 6 shows a top view of one embodiment including a dedicatedfluid line 122. The embodiment may include a thermoelectric cooling(TEC) device 124 for cooling the fluid that circulates throughout thededicated fluid line. Circulation of fluid in the dedicated fluid linemay be driven by a pump. The dedicated fluid line may also be coupled toother components such as heat exchangers.

Similar to FIGS. 1-5, the embodiment may include a support block 126supporting a grid configuration (not visible, under inlet pipes 128 andoutlet pipes 130) capable of separating fluid flow and for coolingsurface areas of the bare die that are not considered hot spots. In thisembodiment, there may be two inlet manifolds 132 to deliver fluid to theinlet pipes. The outlet pipes connect to an outlet manifold 134.Although only one dedicated fluid line is shown, additional hot spotsmay be isolated and additional fluid lines may be dedicated to coolingthose hot spots.

The dedicated fluid line 122 further includes an inlet line 136transporting fluid to the die. The inlet line 136 passes by a cold side138 of TEC device 124 and cooling the fluid inside. The dedicated fluidline 122 further includes an outlet line 140 transporting fluid to thedie. The outlet line 140 passes by a hot side 142 of TEC device 124 andthe fluid in the outlet line cools the hot side of the TEC device.

The cooling fluid used in the dedicated fluid line may be different fromthat of the cooling lines 98. For example, a lubricant-water solutionmay be used in the dedicated fluid line while water is used in thecooling lines. Further, the cooling fluid may be subcooled by the TECdevice. The temperature, flow speed, dimensions, etc. of the dedicatedfluid line may also differ from the parameters used for the coolinglines.

It should be noted that the cooling lines may include segments that alsomay vary depending on size of the bare die and other device parameters.For example, the number of vertical channels, inlet pipes, outlet pipes,inlet manifold, and outlet manifold may vary depending on the number ofdedicated fluid lines. The segments may vary by diameter, length,thickness of material, connectivity, etc.

FIG. 7 shows the exemplary embodiment of FIG. 5 with an alternatemounting method at 150. The embodiment includes a frame 152 forattachment to the substrate 102. A spring 154 is attached to the frame152 and the support block 96. The spring is used to ensure that thevertical channels do not damage the die. There may be additional springs(in addition to the two shown in the figure) distributed around the die,between the bottom of the support block 96 and on top of the frame 152.In this embodiment, instead of epoxy, O-rings 156 may be used as asealant. Standoffs 158 may be used as a spacer to offer additionalstructural support to the die 100.

In one embodiment, although the spring 154 is shown attached to frame152, the frame is not required, and the spring may be directly attachedto the substrate. Further, the spring may include any type of suitablespring and is not limited to the coil spring as pictured.

It is appreciated that the liquid cooling device has been explained withreference to one or more exemplary embodiments, and that the device isnot limited to the specific details given above. References in thespecification made to other embodiments fall within the scope of theclaimed subject matter.

Any reference to device may include a component, circuit, module, or anysuch mechanism in which the device can achieve the purpose ordescription as indicated by the modifier preceding the device. However,the component, circuit, module, or any such mechanism is not necessarilya specific limitation to the device.

Reference in the specification to “an embodiment,” “one embodiment,”“some embodiments,” or “other embodiments” means that a particularfeature, structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments, of the disclosed subject matter. Thevarious appearances of “an embodiment,” “one embodiment,” or “someembodiments” are not necessarily all referring to the same embodiments.

If the specification states a component, feature, structure, orcharacteristic “may”, “might”, or “could” be included, that particularcomponent, feature, structure, or characteristic is not required to beincluded. If the specification or claim refers to “a” or “an” element,that does not mean there is only one of the element. If thespecification or claims refer to “an additional” element, that does notpreclude there being more than one of the additional element.

Those skilled in the art having the benefit of this disclosure willappreciate that many other variations from the foregoing description anddrawings may be made within the scope of the present claimed subjectmatter. Indeed, the claimed subject matter is not limited to the detailsdescribed above. Rather, it is the following claims including anyamendments thereto that define such scope and variations.

1. A liquid cooling device for a die, the device comprising: a pluralityof substantially vertical channels transporting fluid to and from a baredie surface, one or more of the channels comprising: an inlet portiontransporting fluid to the bare die surface, an outlet portion adjacentto the inlet portion and transporting fluid away from the bare diesurface, and a heat transfer region located between the inlet portionand the outlet portion, wherein fluid flowing through the heat transferregion directly contacts the bare die surface and removes heat from thebare die surface; a support block capable of supporting the channels;and a mechanism capable of attaching the support block to a substrate,wherein a plurality of the channels are adjacent to each other.
 2. Theliquid cooling device of claim 1 further comprising one or more inletpipes transporting fluid to the channels and one or more outlet pipestransporting fluid away from the channels.
 3. The liquid cooling deviceof claim 2 wherein the inlet pipes are substantially parallel to theoutlet pipes.
 4. The liquid cooling device of claim 1 wherein the inletportion and the outlet portion are separated by a wall.
 5. The liquidcooling device of claim 1 wherein the heat transfer region isselectively positioned on the bare die surface.
 6. The liquid coolingdevice of claim 5 wherein the heat transfer region is placed over a hotspot on the die.
 7. The liquid cooling device of claim 1 wherein thechannels cover a substantial area of the bare die surface.
 8. The liquidcooling device of claim 1 wherein the channels are configured into agrid to separate flow.
 9. The liquid cooling device of claim 1 whereinthe mechanism comprises a spring coupling the support block to thesubstrate.
 10. The liquid cooling device of claim 1 wherein themechanism comprises epoxy for permanent attachment.
 11. The liquidcooling device of claim 1 further comprising a thermoelectric cooling(TEC) device thermally coupled to one or more of the channels.
 12. Aliquid cooling device for a die, the device comprising: a plurality ofsubstantially vertical channels transporting fluid to and from a baredie surface, one or more of the channels comprising: an inlet portiontransporting fluid to the bare die surface, an outlet portion adjacentto the inlet portion and transporting fluid away from the bare diesurface, and a heat transfer region located between the inlet portionand the outlet portion, wherein fluid flowing through the heat transferregion directly contacts the bare die surface and removes heat from thebare die surface; a support block capable of supporting the channels andcoupling to a substrate; and a dedicated fluid line routing fluid to ahot spot on the bare die surface.
 13. The liquid cooling device of claim12 wherein the dedicated fluid line is routed over a thermoelectriccooling (TEC) device.
 14. The liquid cooling device of claim 13 whereinan outlet line of the dedicated fluid line is routed over a hot side ofthe TEC device and an inlet line of the dedicated fluid line is routedover a cold side of the TEC device.
 15. The liquid cooling device ofclaim 12 wherein the dedicated fluid line comprises a vertical channelwith a heat transfer region above the hot spot.